For the protection of personnel and the environment, oil installations are provided with one or more well bore control devices, such as a riser control device or a blow out preventer, for sealing the well bore.
Some well bore control devices have cutting rams mounted perpendicular to a vertical throughbore. The rams can be activated to sever a tubular disposed in the wellbore and seal the well bore. The cutting rams move through a horizontal plane and are often driven by in-line pistons. These devices have drawbacks however. For example, sealing is generally achieved using elastomeric seals, the limitations of which are being exposed as more aggressive, high-temperature high-pressure, wells are developed.
Improved sealing can be achieved using valves to seal the throughbore, however currently available valves can only successfully cut through a limited range of conduits.